The invention relates to a conventional broad-area laser having a single-mode output through the phenomenon of multimode interference (MMI) in step-index waveguides. Another aspect of the present invention relates to a very robust multi-mode compound cavity laser design that is fully defined by the geometry and the refractive index profile of the MMI region, which is quite insensitive to slight macro-scale refractive index variations due to manufacturing variation or temperature. As the self-imaging position shifts linearly in the refractive index, the confocal beam parameter can be made relatively long.